The surging price of jet fuel isn’t the airline industry’s only problem. Now, it’s whether it will have enough.

Since the U.S. and Israel attacked Iran on Feb. 28, the price of jet fuel in the U.S. has nearly doubled, going from $2.50 a gallon on Feb. 27 to $4.88 a gallon on April 2, with the increases even sharper in other regions. The effective closure of the Strait of Hormuz is choking off supplies of both crude and refined products like jet fuel, further driving up the price.

That’s forcing airlines to consider cutting flights, especially overseas.

Carsten Spohr, CEO of Germany’s Deutsche Lufthansa, told employees in a webcast last week that the carrier is assigning teams to come up with contingency plans because of the war in the Middle East, including for drops in demand or a lack of jet fuel, a spokesman said. Those plans could include grounding some of its aircraft.

The U.S. produces a lot of jet fuel and isn’t as exposed as other regions like Europe and parts of Asia are in comparison. But aircraft fill up locally, so some U.S. airlines could face shortages on international trips.

United Airlines CEO Scott Kirby told reporters late last month that the carrier, which has the most service to Asia among U.S. airlines, would have to cut back its flights there. He also said it’s “not impossible” that airlines collectively would have to reduce service in that region.

He noted that as the price of jet fuel goes up, it could be more acute in parts of the U.S. that aren’t as connected by pipelines.

“There’s not enough refining capacity, and so fuel price prior to this and going forward is more susceptible to supply weakness on the West Coast than anywhere else in the country,” he said.

Kirby told employees earlier in March that the airline is preparing for oil to stay above $100 a barrel through 2027 and is pruning some of its flights in the near term.

“To be clear, nothing changes about our longer-term plans for aircraft deliveries or total capacity for 2027 and beyond, but there’s no point in burning cash in the near term on flying that just can’t absorb these fuel costs,” he said in a March 20 message to employees.

Airlines overall are pruning some flights for the coming months, though they often adjust schedules throughout the year to match demand, aircraft availability or other complications.

Domestic capacity in the second quarter for U.S. carriers is up 2.1%, down from previous plans of 2.3% growth, while total capacity is set to rise 1.1%, down from 2.4% on the week ended March 20, according to a Monday report from UBS.

“We expect more capacity cuts in the coming weeks,” UBS said.

So far, airline executives have said that travel demand is strong, but the fuel strains and price spikes are a headache for carriers and passengers alike as the peak summer travel season approaches.

Fuel is generally airlines’ biggest expense after labor, and carriers are already raising airfare and fees like for checked luggage to make up for the added cost.

Investors will be listening for more insights into how the jet fuel spike could affect the industry as airline earnings kick off Wednesday with Delta Air Lines. That carrier owns a refinery, so it could benefit from jet fuel sales.